Set

A Clojure set is a persistend data structure that holds a unqiue set of elements. Again the elements can be of any type, however each element must be unique for a valid set.

Note Explore creating sets from existing collections. Notice what happens if you have duplicate values in the collection. Define sets directly using the #{} notation and see what happens if there are duplicate values.

  1. (set `(1 2 3 4))
  2. (set `(1 2 1 2 3 4))
  4. #{1 2 3 4}
  5. #{:a :b :c :d}
  6. ;; duplicate key error
  7. #{1 2 3 4 1}

Unique but not ordered

A set is not ordered by the values it contains. If you need a sorted set then you can use the sorted-set function when creating a new set. Or you can run 

  1. (sorted-set 1 4 0 2 9 3 5 3 0 2 7 6 5 5 3 8)
  3. (sort [9 8 7 6 5])
  4. (sort-by )

Looking up values in a set

  1. (#{:a :b :c} :c)
  2. (#{:a :b :c} :z)

Sets can also use the contains? function to see if a value exists in a set

  1. (contains? 
  2.   #{"Palpatine" "Darth Vader" "Boba Fett" "Darth Tyranus"}
  3.   "Darth Vader")